Imaging apparatus incorporated in recent mobile phones and PCs (personal computers) are typically strongly required to have high resolution, low cost, and compactness. Since the cell intervals in CCD (charge coupled device) and CMOS (complementary metal oxide semiconductor) image sensors and other imaging devices have been drastically reduced, an optical system is typically required to have higher imaging performance by suppressing optical aberrations by a greater amount than in related art.
To achieve the requirement described above by simply modifying the optical system, for example, the following problems occur: the number of lenses increases; high assembly precision is typically required; and each lens needs to be manufactured to a thickness that is very difficult to achieve.
To solve the problems, a technology for simplifying each lens by using a spherically curved imaging device to reduce the burden of image plane correction on the optical system has been proposed (see PTL 1, for example).
PTL 1 describes an optical system having a front-diaphragm-type one-group-two-lens configuration in which two lenses separately formed in plastic molding processes are bonded to each other. The technology described in PTL 1 is, however, problematic, for example, in that no infrared removal filter is incorporated and a curved imaging device produces barrel-shaped optical distortion. These problems only allow the optical system to be used with a small pixel number configuration, such as the CIF (common intermediate format) and VGA (video graphics array) standards.
NPL 1 discloses an approach to randomly arranged pixels that allows an imaging device to be curved.